I have looked into the effect would NROL-76 have actually been launched at 11:15 UT on April 30, when the launch was scrubbed.

The effects of a fixed launch time at 11:15 UT rather than a daily launch time shift to match the plane crossing time are actually not that large, it turns out. Note that USA 276 is not exactly in the orbital plane of the ISS (there is a 1.6 degree inclination difference anyway).

To investigate the effect, I adjusted the RAAN of the current orbit accordingly to match launch on 30 April, 11:15 UT..

USA 276 actually then would have made even somewhat closer passes to the ISS (to minimum distances less than 15 km on June 3 near 18:44 UT), but with the approach times some 4 hours shifted compared to those for the actual launch date.

This launch was originally scheduled to launch on April 16 at a very similar 7 am window. I am nowhere near knowledgeable enough to figure this out so I'll leave it to somebody else, but what is the implication for it's orbit relative to the ISS had it launched as intended 2 weeks earlier? Could it be that the reason for the "large" delay was because a couple day slide would have screwed up the orbital timing to place the satellite and the ISS in proximity so they delayed for longer to make them sync up again? Sort of a "if it has to slide 3 days, then it has to slide 14 days to make it all work properly, so since the payload is delayed 3 days we launch in 14!" kind of deal?? I'm throwing pasta against the wall here to see if anything sticks so somebody that knows the orbital mechanics see if any of that makes sense.

While browsing the website of Ball Aerospace, the company that built USA 276, I found that they also have built RAVEN, an instrument delivered to and installed on the outside of the ISS in February this year.

So, let that sink in: Ball Aerospace, the company that built USA 276, a spacecraft that appears to be secretly moving towards a series of clandestine very close approaches to the ISS, also built RAVEN, an experiment installed on the ISS to monitor close approaching spacecraft.

NROL-76 is said to have been part of a "delivery to orbit" contract: e.g. the spacecraft and its launch is the responsibility of the builder (Ball Aerospace, who hired SpaceX for the launch), who hands over the spacecraft to the customer (the NRO) once in operational orbit. The question now is, is USA 276 at this stage still operated by Ball Aerospace, or has it been handed over to the NRO already?

A few minutes ago, the ISS had a pass at my position and I waited for USA 276 to come after her. And sure enough it did, on the same path just 1 to 2 minutes (didnt watch a clock, didn't want to ruin my night vision) after the ISS. It was easily visible by naked eye, no gear necessary. Will be fun to look for it tomorrow when it is much closer. A shame that it doesn't form a triplet with Dragon.

While browsing the website of Ball Aerospace, the company that built USA 276, I found that they also have built RAVEN, an instrument delivered to and installed on the outside of the ISS in February this year.

So, let that sink in: Ball Aerospace, the company that built USA 276, a spacecraft that appears to be secretly moving towards a series of clandestine very close approaches to the ISS, also built RAVEN, an experiment installed on the ISS to monitor close approaching spacecraft.

NROL-76 is said to have been part of a "delivery to orbit" contract: e.g. the spacecraft and its launch is the responsibility of the builder (Ball Aerospace, who hired SpaceX for the launch), who hands over the spacecraft to the customer (the NRO) once in operational orbit. The question now is, is USA 276 at this stage still operated by Ball Aerospace, or has it been handed over to the NRO already?

The Raven lidar is nearly identical to the Orion NSS lidar flown on the STS-134 STORRM mision. It was designed for >5 km range to a "cooperative" target, but the imaging aspect to the lidar is only useful below a few hundred meters. NASA could be expected object strenuously if NRO brought NROL-76 close enough for Raven to observe in detail.

Besides, what would be learned? The Raven mission has shown how to make hardware invisible to lidar.(Hint: Look for the lidar images of the CRS-10 Dragon. The shiny solar panels are not visible.)

Plus the Raven program is NASA, and NROL-76 is from the NRO. (of course) It is hard to imagine an NRO mission that depended on an instrument owned and run by another agency. Even different NASA centers have trouble collaborating like that. I once tried to float a mission concept to do something that would be observed by sensors on a previously launched spacecraft and got major pushback. You can't control those other instruments, or be assured they will function.

While browsing the website of Ball Aerospace, the company that built USA 276, I found that they also have built RAVEN, an instrument delivered to and installed on the outside of the ISS in February this year.

So, let that sink in: Ball Aerospace, the company that built USA 276, a spacecraft that appears to be secretly moving towards a series of clandestine very close approaches to the ISS, also built RAVEN, an experiment installed on the ISS to monitor close approaching spacecraft.

NROL-76 is said to have been part of a "delivery to orbit" contract: e.g. the spacecraft and its launch is the responsibility of the builder (Ball Aerospace, who hired SpaceX for the launch), who hands over the spacecraft to the customer (the NRO) once in operational orbit. The question now is, is USA 276 at this stage still operated by Ball Aerospace, or has it been handed over to the NRO already?

The Raven lidar is nearly identical to the Orion NSS lidar flown on the STS-134 STORRM mision. It was designed for >5 km range to a "cooperative" target, but the imaging aspect to the lidar is only useful below a few hundred meters. NASA could be expected object strenuously if NRO brought NROL-76 close enough for Raven to observe in detail.

Besides, what would be learned? The Raven mission has shown how to make hardware invisible to lidar.(Hint: Look for the lidar images of the CRS-10 Dragon. The shiny solar panels are not visible.)

Plus the Raven program is NASA, and NROL-76 is from the NRO. (of course) It is hard to imagine an NRO mission that depended on an instrument owned and run by another agency. Even different NASA centers have trouble collaborating like that. I once tried to float a mission concept to do something that would be observed by sensors on a previously launched spacecraft and got major pushback. You can't control those other instruments, or be assured they will function.

So let that sink..... beneath the waves.

edit: corrected an error in units

So you expect the NRO to publicly reveal if they have an interest in Raven, that doesn't seem very likely does it?

I think I'm going to go back to occam's razor. 51 degrees, with the exception of Russia, Canada, Northern Europe, and Southern Argentina/Chile provides coverage of the entire world, and all the hot spots in the modern world. No, I think we can ignore Putin. I am beginning to suspect that it's special relationship with ISS is nothing more than a red herring.

I do wonder is someone thought, the special relationship would make it difficult for people to find and track post launch. But that would be silly, it's very hard to hide in low Earth orbit.

I think I'm going to go back to occam's razor. 51 degrees, with the exception of Russia, Canada, Northern Europe, and Southern Argentina/Chile provides coverage of the entire world, and all the hot spots in the modern world. No, I think we can ignore Putin. I am beginning to suspect that it's special relationship with ISS is nothing more than a red herring.

I do wonder is someone thought, the special relationship would make it difficult for people to find and track post launch. But that would be silly, it's very hard to hide in low Earth orbit.

While browsing the website of Ball Aerospace, the company that built USA 276, I found that they also have built RAVEN, an instrument delivered to and installed on the outside of the ISS in February this year.

So, let that sink in: Ball Aerospace, the company that built USA 276, a spacecraft that appears to be secretly moving towards a series of clandestine very close approaches to the ISS, also built RAVEN, an experiment installed on the ISS to monitor close approaching spacecraft.

NROL-76 is said to have been part of a "delivery to orbit" contract: e.g. the spacecraft and its launch is the responsibility of the builder (Ball Aerospace, who hired SpaceX for the launch), who hands over the spacecraft to the customer (the NRO) once in operational orbit. The question now is, is USA 276 at this stage still operated by Ball Aerospace, or has it been handed over to the NRO already?

I have an alternate theory: if USA 276 being on the same orbit as the ISS is not coincidental, it's not because it's using the ISS as a target, but because it is using the ISS as cover.

Think about it:* The NRO has concentrated its capabilities on a few satellites. In low orbit, there's something like 3 KH-11s, 4 Topaz radar sats, and maybe 3 operational Intruder emitter-location pairs. * Russia and China have demonstrated, and probably operational, ASAT capabilities.* As an opening move in a large conflict, they could use them against an US constellation to gain a military advantage: if they destroy one Intruder in each pair, the US loses its overhead emitter location capability (if high-orbit satellites cannot pick up the job). * Because those satellites are on unusual orbits, and because they are unmanned, the political cost of shooting them down is limited: There will be no US soldiers killed, and it will generate a lot of orbital debris, but not on the most crowded orbits, so the consequences might be far away.* The NRO knows this, and has been looking at ways to counter it, such as disaggregation. The problem is there is no way to split up a large instrument on many cubesats, so big, expensive birds are here to stay.* So the NRO is looking for ways to make its satellites harder to shoot down. Stealth is an option, but it makes the satellites extremely expensive. The other option is to put the satellites behind cover, but there's no cover in space.* Enter the ISS. A 100 billion $, multinational, manned space station. If the USA puts a satellite in a close orbit, and if this satellite is shot down, the resulting debris have a high chance of impacting and maybe destroying the ISS. If Russia is the shooter, it is putting its own investment at risk. If it is China, it is destroying the property of parties external to the conflict (Russia and European states are unlikely to be directly involved in an US-China war). In both cases, astronauts lives are at risk if they do not evacuate quickly, and the debris cloud keeps the station at risk, making it too risky for further use. This massively increases the political cost of shooting the satellite.* So the adversary does not shoot the ISS-coorbital satellite. It can still provide intelligence throughout the conflict, even if the handful of other NRO satellites are shot down.

I think I'm going to go back to occam's razor. 51 degrees, with the exception of Russia, Canada, Northern Europe, and Southern Argentina/Chile provides coverage of the entire world, and all the hot spots in the modern world. No, I think we can ignore Putin. I am beginning to suspect that it's special relationship with ISS is nothing more than a red herring.

I do wonder is someone thought, the special relationship would make it difficult for people to find and track post launch. But that would be silly, it's very hard to hide in low Earth orbit.

What are you going to say if it manoeuvres to keep in step with ISS?

Staying with ISS to maintain the confusion while keeping actual mission unclear? Or what gosnold said

I have an alternate theory: if USA 276 being on the same orbit as the ISS is not coincidental, it's not because it's using the ISS as a target, but because it is using the ISS as cover.

Think about it:* The NRO has concentrated its capabilities on a few satellites. In low orbit, there's something like 3 KH-11s, 4 Topaz radar sats, and maybe 3 operational Intruder emitter-location pairs. * Russia and China have demonstrated, and probably operational, ASAT capabilities.* As an opening move in a large conflict, they could use them against an US constellation to gain a military advantage: if they destroy one Intruder in each pair, the US loses its overhead emitter location capability (if high-orbit satellites cannot pick up the job). * Because those satellites are on unusual orbits, and because they are unmanned, the political cost of shooting them down is limited: There will be no US soldiers killed, and it will generate a lot of orbital debris, but not on the most crowded orbits, so the consequences might be far away.* The NRO knows this, and has been looking at ways to counter it, such as disaggregation. The problem is there is no way to split up a large instrument on many cubesats, so big, expensive birds are here to stay.* So the NRO is looking for ways to make its satellites harder to shoot down. Stealth is an option, but it makes the satellites extremely expensive. The other option is to put the satellites behind cover, but there's no cover in space.* Enter the ISS. A 100 billion $, multinational, manned space station. If the USA puts a satellite in a close orbit, and if this satellite is shot down, the resulting debris have a high chance of impacting and maybe destroying the ISS. If Russia is the shooter, it is putting its own investment at risk. If it is China, it is destroying the property of parties external to the conflict (Russia and European states are unlikely to be directly involved in an US-China war). In both cases, astronauts lives are at risk if they do not evacuate quickly, and the debris cloud keeps the station at risk, making it too risky for further use. This massively increases the political cost of shooting the satellite.* So the adversary does not shoot the ISS-coorbital satellite. It can still provide intelligence throughout the conflict, even if the handful of other NRO satellites are shot down.

Nah, it couldn't be a high value asset. It was a small spacecraftand it was not put an a useful orbit to provide the information that high value assets provide